Big dinosaurs steered clear of the tropics

NSF | JUNE 21, 2015

For more than 30 million years after dinosaurs first appeared, they remained inexplicably rare near the equator, where only a few small-bodied meat-eating dinosaurs made a living. Scientists have developed a new explanation: rapid vegetation changes related to climate fluctuations between arid and moist climates and the resulting extensive wildfires of the time.

Triassic Mural. Image credit: Carl Malamud/Wikimedia (CC BY 2.0)

According to scientists who pieced together a detailed picture of the climate and ecology more than 200 million years ago at Ghost Ranch in northern New Mexico, a site rich with fossil, the tropical climate swung wildly with extremes of drought and intense heat. Wildfires swept the landscape during arid regimes and reshaped the vegetation available for plant-eating animals.

It was a time of climate extremes that went back and forth unpredictably. Large, warm-blooded dinosaurian herbivores weren't able to exist close to the equator--there was not enough dependable plant food.

The conditions would have been something similar to the arid western United States today, although there would have been trees and smaller plants near streams and rivers, and forests during humid times.

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